The present invention relates to a device for releasing finely divided bubbles of a gas into a liquid placed in a container and diffusing the bubbles through the entire body of the liquid.
The term "inert gas" as used herein and in the appended claims includes argon gas, helium gas, krypton gas and xenon gas of the Periodic Table and also nitrogen gas which is inert to aluminum and aluminum alloys.
There are cases wherein a gas needs to be released into a liquid in the form of finely divided bubbles. For example, a treating gas must be released into molten aluminum or a molten aluminum alloy in the form of bubbles in order to remove from the melt dissolved hydrogen gas, nonmetallic inclusions such as aluminum and magnesium oxides, and alkali metals such as potassium, sodium and phosphorus. Further for an accelerated chemical reaction, a gas is released into a liquid in the form of bubbles to contact the gas with the liquid. To assure satisfactory contact between the gas and the liquid in these cases, it is required to finely divide bubbles to the greatest possible extent and diffuse the bubbles into the liquid uniformly.
Accordingly, a device has heretofore been used which comprises a vertical rotary shaft disposed in a container for a liquid and internally formed with an axial gas supply channel, and a rotor attached to the lower end of the shaft. The gas supply channel has an open lower end at the bottom surface of the rotor. The rotor is formed in its bottom surface with a plurality of grooves extending radially from the channel open end to the periphery of the bottom. In the peripheral surface of the rotor where the radial grooves have there openings, vertical grooves are formed each of which has a lower end communicating with the radial groove and an open upper end at the top surface of the rotor (see U.S. Pat. No. 3,227,547, FIGS. 14 and 15). When the rotary shaft is rotated by drive means while a gas is being supplied from the gas supply channel to the radial grooves in the bottom surface of the rotor, the gas flows in the centrifugal direction through the radial grooves into the vertical grooves in the peripheral surface of the rotor, from which the gas is released into the liquid in the form of finely divided bubbles.
However, our research and experiments have revealed that the conventional device is not satisfactory in its bubble dividing and diffusing effects for the following reason. When the rotor is rotated, the liquid in the container flows also in the same direction as the rotor at a speed lower than the speed of rotation of the rotor. The greater the difference between the two speeds, the greater is the bubble dividing action. Nevertheless, the speed difference of the conventional device is not very great because the radial grooves in the bottom surface of the rotor are in communication with the vertical grooves in the peripheral surface. Moreover, if the amount of gas to be released increases, the vertical grooves, which are filled with the gas, encounter difficulty in producing finely divided bubbles and fail to exert a sufficient agitating action and to diffuse the bubbles into the liquid efficiently.